This invention relates to an apparatus for testing electric motor performance, and more particularly to an apparatus for testing the power performance of an electric motor for an electric vehicle.
Generally, when evaluating the performance of an electric motor (hereinafter referred to as a test motor) on a test bench, performance testing is carried out under two different evaluation circumstances, i.e. evaluation under constant conditions (with constant revolution and constant torque) and evaluation under acceleration/deceleration operations. Test driving with acceleration/deceleration operations further includes a simple driving pattern and a mode simulating for actual travel of a vehicle. Under the simulation mode, the motor revolution is controlled so that the vehicle speed indicates a predetermined running pattern (for example, LA#4 mode based on actual driving in Los Angeles, Calif.), while generating a resistance corresponding to an actual running resistance using a load motor.
Controlling of the running resistance is carried out by computing a load on the vehicle based on the revolution of the test motor (i.e. vehicle speed) and outputting the computed load value to the load motor. The load motor has a computing unit for calculating the running resistance in its control system.
Conventionally, several techniques are known for calculating running resistance. One technique is to calculate a load from a load map which is preset in response to a vehicle speed. In this case, the test bench should be provided with an element having an inertia equivalent to the vehicle inertia (e.g. a flywheel) and resistance equivalent to the vehicle speed is applied to the test apparatus as a load.
Alternatively, load may be calculated based on a feedback speed/acceleration of the load motor, vehicle weight, air resistance factor, etc. When carrying out a performance test on a test bench using this technique, feedback speed and acceleration of the load motor must be accurately measured to provide an appropriate load in accordance with the measurement result.
Japan Laid Open (Kokai) H3-212194 discloses a structure of outputting a speed command (torque command) to the test motor in accordance with a travelling schedule of the vehicle, while outputting to the load motor a resistance (torque) corresponding to travelling conditions at the feedback speed and acceleration. Each of the operations are controlled by a microcomputer.
However, in the former technique using a flywheel, the mechanical strength of the test bench must be reinforced in order to mount the flywheel, which causes the test apparatus to become larger as well as more expensive.
On the other hand, in calculating a load based on the feedback speed and acceleration of the load motor (in the latter technique), it is difficult to detect an acceleration with high accuracy due to the influence of discrete errors in digital systems and the influence of noise in analogue systems. The detection error in acceleration may provide an unrealistic load value and prevent the providing of an appropriate running resistance.
Furthermore, presence of time delay is inevitable during the measurement of the fedback speed and acceleration, and it adversely affects reproduction of the measured value. In order to reduce the time delay, the accuracy of the microcomputer must be improved, which results in increased cost.